Methods are available for preventing unauthorized manipulation of a control program stored in a control device of a motor vehicle or manipulation of parameters or limiting values. The control program may control or regulate specific functions (or units) in the motor vehicle, for example, an internal combustion engine, a driving dynamics regulator, a stop control system (SCS), or an electronic steering system (steer-by-wire). The control program may be stored in a re-writable memory assembly, for example, a flash memory. A manipulation of the control program, the parameters, or the limiting values may cause a defect and/or change in the mode of operation of the controlled or regulated unit. Therefore, manipulation of the control program, parameters, or the limiting values should be prevented, but, if not prevented, the manipulation should at least be capable of detection, so that, for example, the cause of a defect of a controlled or regulated unit may be established or, for example, so that warranty claims may be correctly assigned.
Although unauthorized persons may be able to manipulate the control program, the parameters, or the limiting values, access to the memory assembly of the control device should not be completely forbidden. For example, to perform reprogramming of the control device, an authorized user group should be able to access the memory assembly. Furthermore, it may be necessary to store a new version of a control program or new parameters or limiting values in the control device, for example, to remove errors in the software or to consider new legal requirements.
As referred to in German Published Patent Application No. 197 23 332, a checksum of the content or of part of the content of the re-writable memory should be formed and compared with a reference checksum to check data stored in a re-writable memory of a motor vehicle controller for manipulation. The reference checksum is determined on the basis of data that should be programmed before the control device is programmed, and is stored in the re-writable memory of the control device. If the checksum and the comparison checksum do not match, manipulation of the data is presumed and the control device is blocked for further operation. However, it is believed that this method may not detect all manipulations in a stored control program. In addition, it is believed that this method may be intentionally manipulated in a simple manner, to disable blocking of the control device. Furthermore, control devices, which are manipulated in this manner, may easily be operated with manipulated data, for example, with a manipulated control program.